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Title: High Resolution 15N NMR of the 225 K Phase Transition of Ammonia Borane (NH3BH3): Mixed Order-Disorder and Displacive Behavior

Abstract

We report high resolution 15N NMR probing of the solid-solid phase transition of 15N-labeled ammonia borane (NH3BH3) around 225 K. Both the 15N isotropic chemical shift, δiso, and the spin-lattice relaxation rate (T1-1) exhibited strong anomalies around 225 K. The analysis of T1-1 using the Bloembergen-Purcell and Pound model showed that the motional correlation time, τ, increased from about 1 ps to 100 ps while the corresponding Arrhenius activation energy increased from 6 to 13.4 kJ/mol on going through the transition. The observed strong temperature dependence of δiso was interpreted by an extension of the Bayer model. The time scale of the underlying motion was found to be in a reasonable agreement with the T1-1 data. These results imply that the NH3 rotor motion plays a pivotal role in the transition mechanism, and that the transition is of both order-disorder and displacive type. This work was supported by the Office of Basic Energy Sciences of the U. S. Department of Energy Chemical Sciences program. Pacific Northwest National Laboratory is operated by Battelle for the U. S. Department of Energy.

Authors:
; ; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
901463
Report Number(s):
PNNL-SA-52116
KC0302010; TRN: US200714%%22
DOE Contract Number:
AC05-76RL01830
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Physical Chemistry B, 111(4):677-681; Journal Volume: 111; Journal Issue: 4
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; AMMONIUM COMPOUNDS; BORANES; ACTIVATION ENERGY; CHEMICAL SHIFT; RESOLUTION; SPIN-LATTICE RELAXATION; NUCLEAR MAGNETIC RESONANCE; PHASE TRANSFORMATIONS; 15N NMR; ammonia borane; phase transition

Citation Formats

Gunaydin-Sen, Ozge, Achey, Randall, Dalal, Nar S., Stowe, Ashley C., and Autrey, Thomas. High Resolution 15N NMR of the 225 K Phase Transition of Ammonia Borane (NH3BH3): Mixed Order-Disorder and Displacive Behavior. United States: N. p., 2007. Web. doi:10.1021/jp0649347.
Gunaydin-Sen, Ozge, Achey, Randall, Dalal, Nar S., Stowe, Ashley C., & Autrey, Thomas. High Resolution 15N NMR of the 225 K Phase Transition of Ammonia Borane (NH3BH3): Mixed Order-Disorder and Displacive Behavior. United States. doi:10.1021/jp0649347.
Gunaydin-Sen, Ozge, Achey, Randall, Dalal, Nar S., Stowe, Ashley C., and Autrey, Thomas. Thu . "High Resolution 15N NMR of the 225 K Phase Transition of Ammonia Borane (NH3BH3): Mixed Order-Disorder and Displacive Behavior". United States. doi:10.1021/jp0649347.
@article{osti_901463,
title = {High Resolution 15N NMR of the 225 K Phase Transition of Ammonia Borane (NH3BH3): Mixed Order-Disorder and Displacive Behavior},
author = {Gunaydin-Sen, Ozge and Achey, Randall and Dalal, Nar S. and Stowe, Ashley C. and Autrey, Thomas},
abstractNote = {We report high resolution 15N NMR probing of the solid-solid phase transition of 15N-labeled ammonia borane (NH3BH3) around 225 K. Both the 15N isotropic chemical shift, δiso, and the spin-lattice relaxation rate (T1-1) exhibited strong anomalies around 225 K. The analysis of T1-1 using the Bloembergen-Purcell and Pound model showed that the motional correlation time, τ, increased from about 1 ps to 100 ps while the corresponding Arrhenius activation energy increased from 6 to 13.4 kJ/mol on going through the transition. The observed strong temperature dependence of δiso was interpreted by an extension of the Bayer model. The time scale of the underlying motion was found to be in a reasonable agreement with the T1-1 data. These results imply that the NH3 rotor motion plays a pivotal role in the transition mechanism, and that the transition is of both order-disorder and displacive type. This work was supported by the Office of Basic Energy Sciences of the U. S. Department of Energy Chemical Sciences program. Pacific Northwest National Laboratory is operated by Battelle for the U. S. Department of Energy.},
doi = {10.1021/jp0649347},
journal = {Journal of Physical Chemistry B, 111(4):677-681},
number = 4,
volume = 111,
place = {United States},
year = {Thu Feb 01 00:00:00 EST 2007},
month = {Thu Feb 01 00:00:00 EST 2007}
}
  • Raman spectra of single crystal ammonia borane, NH3BH3, were recorded as a function of temperature from 77 to 300 K using Raman microscopy and a variable temperature stage. The orthorhombic to orientationally disordered tetragonal phase transition at 225 K was clearly evident from the decrease in the number of vibrational modes. However some of the modes in the orthorhombic phase appeared to merge 10 to 12 K below the phase transition perhaps suggesting the presence of an intermediate phase. Factor group analysis of vibrational spectra for both orthorhombic and tetragonal phase is provided. To our knowledge this is first reportedmore » vibrational spectra in the BH and NH stretching region of single crystal NH3BH3 in the orthorhombic phase.« less
  • The structure of deuterated ..cap alpha..-terephthalic acid C/sub 6/D/sub 4/(COOD)/sub 2/ is triclinic (low-temperature lattice constants: a = 7.70 A, b = 6.34 A, c = 3.66 A, ..cap alpha.. = 92.98/sup 0/, ..beta.. = 107.88/sup 0/, ..gamma.. = 94.60/sup 0/, space group P/sup 1/). It has been refined to R/sub I/ approx. 7% from high-resolution reactor neutron powder data (D1A/ILL, Grenoble) at 2, 82, and 300 K. It has also been refined from high-resolution time-of-flight pulsed neutron source data (SEPD/IPNS, Argonne) at 15 and 80 K to R/sub I/ approx. 6%. Concerning the acid hydrogen and the carbon-oxygen doublemore » bond the structure is almost fully disordered at 300 K. At low temperature there is a gradual transition to an ordered arrangement of almost linear O-D ... O (angle = 178/sup 0/) acid hydrogen bonds (O-D = 1.01 A, D ... O = 1.62 A; order parameter approx. 1 below approx. 80 K). Both time-of-flight and constant wavelength data reveal a sample-contributed peak broadening which results either from strain or a small departure from the assumed structure. This systematic error in the data degrades the reliability of both the constant wavelength and time-of-flight refinements such that standard deviations of structural parameters do not overlap to the expected degree. 27 references, 5 figures, 3 tables.« less
  • We use time-of-flight neutron powder diffraction to examine static displacive disorder in three different pyrochlore A{sub 2}B{sub 2}O{sub 6}O' compounds with Bi on the A site. The compounds (Bi{sub 1.5}Zn{sub 0.5})(Nb{sub 1.5}Zn{sub 0.5})O{sub 6}O' (BZN) (Bi{sub 1.5}Zn{sub 0.5})(Ta{sub 1.5}Zn{sub 0.5})O{sub 6}O' (BZT), and (Bi{sub 1.5}Zn{sub 0.5})(Sb{sub 1.5}Zn{sub 0.5})O{sub 6}O' (BZS), are of interest - particularly BZN - for their high dielectric constants in the absence of any phase transition from the cubic high temperature phase. The local structures of the three compounds is characterized by displacive disorder from the ideal pyrochlore positions for both the A and O' sites, withmore » the precise nature of the disorder being quite similar. However the extent of displacive disorder is different, despite the B-O networks being nearly identical in the three compounds. The reported dielectric constants of the three compounds are related to the extent of local displacement, and BZN, with the largest extent of local atomic displacement of A and O', is also reported to have the largest dielectric constant at 1 MHz. The dielectric constants are also related to the magnitudes of the thermal parameters of the different ions. The strongest correlation is found to involve the thermal parameter on the B site (Nb, Ta, or Sb)« less